Method for in-situ utilization of fuels by combustion

ABSTRACT

Subsurface combustible material, such as coal, can be burned in situ by providing a number of passages which extend downwardly from the surface and which extend to, and generally horizontally through, the combustible material, by forming a combustion chamber within said combustible material adjacent to and in communication with the ends of said passages, and by using one of said passages to supply air to said combustion chamber while using another of said passages to remove products of combustion from said combustion chamber. The wall of said combustion chamber, which is adjacent the inner ends of said passages, will progressively burn away, and thus cause said combustion chamber to &#39;&#39;&#39;&#39;move&#39;&#39;&#39;&#39; toward said passages; and the overburden adjacent said wall will provide a self-supporting overhang which will enable air to continue to enter said combustion chamber from said one passage and will enable products of combustion to move to and outwardly through said other of said passages - even though the overburden adjacent the opposite wall of said combustion chamber slumps down into said combustion chamber adjacent to said opposite wall, reach the area where that combustible material is being burned.

United States Patent [-72] Inventor Howard V.- Sears Flat River, Mo.[21] Appl. No. 809,571 [22] Filed Mar. 24, 1969 [45] Patented Feb. 16,1971 [73] Assignee St. Joe Minerals Corporation New York, N .Y.

[54] METHOD FOR lN-SlTU UTILIZATION OF FUELS BY COMBUSTION 15 Claims, 7Drawing Figs.

[52] us. Cl 299 2; 166/259; 175/12 [51] lnt.Cl E2lc 43/00 [50] FieldofSearch 299/2, 4, 5; 175/12; l66l256-259 [56] References Cited UN lTEDSTATES PATENTS 947,608 l/19l0 Betts 299/2 1,992,323 2/1935 Ranney 299/22,841,375 7/1958 Salomonsson 175/12X 3,223,158 12/1965 Baker 166/259Primary Eicaminer- Ernest R. Purser Attorney- -Kingsland Rogers,Eze'l-l, Eilersand Robbins ABSTRACT: Subsurface combustible material,such as coal, can be burned in situ by providing a number of passageswhich extend downwardly from the surface and which extend to, andgenerally horizontally through, the combustible material, by forming acombustion chamber within said combustible material adjacent to and incommunication with the ends of said passages, and by using one of saidpassages to supply air to said combustion chamber while using another ofsaid passages to remove products of combustion from said combustionchamber. The wall of said combustion chamber, which is adjacent theinner ends of said passages, will progressively burn away, and thuscause said combustion chamber to move toward said passages; and theoverburden adjacent said wall will provide a self-supporting overhangwhich will enable air to continue to enter said combustion chamber fromsaid one passage and will enable products of combustion to move to andoutwardly through said other of said passages even though the overburdenadjacent the opposite wall of said combustion chamber slumps down intosaid combustion chamber adjacent to said opposite wall, reach the areawhere that combustible material is being burned.

[ PATENTEUFEBI slsm 3563.606

SHEET 1 OF 2 24/ FIG. 5.

METHOD FOR IN-SITU UTILIZATION OF FUELS BY COMBUSTION This inventionrelates to improvements in Mining. More particularly, this inventionrelates to improvements in methods of burning subsurface combustiblematerial in situ.

It is, therefore, an object of the present invention to provide animproved method of burning subsurface combustible material in situ.

The cost of mining subsurface combustible material, such as coal, ishigh where that combustible material must be mined at the working facesof shafts. The strip mining of subsurface combustible material isexpensive where that combustible material is located an appreciabledistance below the surface, and it is expensive where governmentalagencies require the mined area to be restored to a state approximatingits original state. The expense and other disadvantages of miningsubsurface combustible material by driving shafts and by stripping couldbe obviated if a commercially practical method of buming subsurfacecombustible material in situ could be developed. In recognition of thisfact, very large sums of money have been expended in attempts to developcommercially practical methods of buming-subsurface combustible materialin situ; but those attempts have been unavailing. Consequently, it wouldbe desirable to provide a commercially practical method of burningsubsurface combustible material in situ. The present invention providessuch a method; and it does by forming a number of passages so theyextend downwardly from the surface to a seam of combustible material andthen extend substantial distances through that seam in a generallyhorizontal direction. It is, therefore, an object of the presentinvention to form a number of passages so they extend downwardly fromthe surface to a seam of combustible material and then extendsubstantial distances through that scam in a generally horizontaldirection.

Several prior attempts to develop commercially practical methods ofburning subsurface combustible material in situ have utilized verticallydirected passages which extended downwardly from the surface to theseams of combustible material; and the combustible material was causedto burn away from the lower ends of those passages. Unfortunately, afterthe combustible material burns away any appreciable distances from thelower end of a vertically directed passage, part of the overburden tendsto fall into the space between that lower end and the unburnedcombustible material. The resulting rubble tends to, and frequentlywill, so impede the supplying of further air to the burning combustiblematerial, and to so impede the removal of products of combustion, thateffective combustion of the remaining combustible material can not besustained. However, with the passages provided by the present invention,the combustible material will burn toward, as well as away from, theinner ends of those passages; and hence the rubble, that develops aspart of the overburden falls into the space previously occupied by thecombustible material, will fall behind the burning combustible materialand will not fall between that burning combustible material and theinner ends of the passages. Because the overburden will usually haveenough structural strength to provide a self-supporting overhang ofseveral feet in width,after the combustible material beneath it has beenburned, the rubble which develops as the overburden falls into the spacepreviously occupied by the combustible material will usually be severalfeet away from the inner ends of the horizontally directed portions ofthe passageways. The resulting space between the rubble and the innerends of the horizontally directed portions of the passageways willenable some of those passages to continue to supply air to, and willenable other of those passages to continue to withdraw products ofcombustion from, the combustible material; and hence the passagesprovided by the present invention make it practical to burn subsurfacecombustible material in situ.

Where subsurface mining is done by driving shafts, one serious hazard isthe existence of pockets of noxious gases, such asas the shafts approachthose pockets. The present invention makes subsurface mining, which isdone by driving shafts, safer by forming passages which extend into theseams ahead of the shafts and by maintaining reduced pressures withinthose passages. If any pockets of noxious gases exist in the seams aheadof the shafts and if those pockets are intersected by the passages ofthe present invention, the reduced pressures within those passages willwithdraw the noxious gases from those pockets, and thus will keep thosenoxious gases from those pockets, and thus will keep those noxious gasesfrom entering the shafts as the-shafts progress to the areas containingthose pockets. Even where the passages of the present invention do notintersect the gas-filled pockets, the reduced pressures within thosepassages will tend to draw any noxious gases from those pockets throughfissures, cracks or porous areas in the seams. In the event the seamsare free of fissures, cracks and porous areas, the reduced pressureswithin the passages can still withdraw noxious gases from pockets withinthose seams where blasting charges at the working faces of the shaftsdevelop cracks and fissures in those seams. As a result, the forming ofpassages which extend down into a seam ahead of a shaft driven into thatseam, and the maintaining of reduced pressures within those passages,can minimize and even eliminate the hazards of noxious gases. It is,therefore, an object of the present invention to form passages whichextend down into a seam ahead of a shaft driven into that seam and tomaintain reduced pressures within those passages.

Other objects and advantages of the present invention should becomeapparent from an examination of the drawing and accompanyingdescription.

In the drawing and accompanying description two preferred embodiments ofthe present invention are shown and described but it is to beunderstoodthat the drawing and accompanying description are for thepurpose of illustration only and do not limit the invention and that theinvention will be defined by the appended claims.

In the drawing FIG. I is a diagrammatic plan view of an area whichoverlies a seam of subsurface combustible material, and it indicates bydotted lines a number of passages which extend downwardly from thesurface to that seam;

FIG. 2 is a sectional view through the area shown in FIG. I, and it istaken along the plane indicated by the line 22 in FIG. I; i

FIG. 3 is another sectional view through the area shown in F IG. 11, andit is taken along the plane indicated by the line 3-3 in FIG. I;

FIG. 4 is a sectional view which is comparable to the righthand portionof FIG. 3 after part of the combustible material of the seam has beenburned away;

FIG. 5 is a sectional view which is similar to FIG. 4, but it shows howrubble has filled part of the area where combustible material of theseam has burned away;

FIG. 6 is a diagrammatic view of a mine shaft and of passages formedahead of that mine shaft; and

FIG. 7 is a sectional view that is taken along the plane indicated bythe line 7-7 in FIG. 6.

Referring to the drawing in detail, the numeral 20 generally denotes anarea which has a seam 22 of coal located beneath the surface. That seamof coal is overlain by an overburden 24 of rock, clay, top soil, or thelike; and that seam of coal may be many thousands of feet long and maybe many hundreds of feet wide. The numerals 21, 25 and 29 denotepassages which extend downwardly from the surface of the area 20,through the overburden 24, and into the seam 22 of coal. Those openingsextend downwardly from the surface of the area 20 to, and then extendhorizontally through, the seam 22 of coal. The passages 21, 25 and 29can be arcuate, in part, or they can incline downwardly to the seam 22.The inner end of the passage 25 laps part of the horizontally extendingportion of the passage 29, and the inner end of the passage 21 laps partof the horizontally directed portion of the passage 25. In practice, thehorizontally extending portion of each of the passages 21, 25 and 29 maybe several hundred feet long. The lapped portions of adjacent passageswill preferably be coextensive for distances in the range of 20 to 50feet. The lapped portions of adjacent passages can be spaced apartappreciable distances; but, preferably, those lapped portions will belocated within a few feet of each other.

The numerals 26, 30 and 34 denote further passages which extenddownwardly from the surface to the seam 22. The passages 21, 25 and 29plus other passages, not shown, define a row of passages; and thepassages 26, 30 and 34 plus other passages, not shown, define a secondrow of passages. The numerals 36, 40 and 44 denote further passageswhich extend downwardly from the surface to the seam 22; and thosepassages plus other passages, not shown, define a third row of passages.The numerals 46, 50 and 54 denote further passages which extenddownwardly from the surface to the seam 22; and those passages plusother passages, not shown, define a fourth row of passages. The numerals56, 60 and 64 denote further passages which extend downwardly from thesurface to the seam 22; and those passages plus other passages notshown, define a fifth row of passages. The five rows of passages denotedby the hereinbefore-enumerated numerals are representative of many rowsof passages which are formed in the overburden 24 and which extend intothe seam 22; and those rows will extend throughout the entire portion ofthe area where the combustible material of the seam 22 is to be burned.The various rows of passages will preferably be spaced apart distancesin the range of 30 to 50 feet.

The numerals 65, 68 and 72 denote additional passages which extenddownwardly from the surface to the seam 22; and those passages plusother passages, not shown, define a row of passages which extendstransversely of the previously described rows of passages in the area20. The inner end of the passage 65, while crossing the inner ends ofthe passages 29 and 34, laps part of the horizontally directed portionof the passage 68; and the inner end of the passage 68, while crossingthe inner ends of the passages 44 and 54, laps part of the horizontallydirected portion of the passage 72. The numerals 73, 76 and 80 denotestill further passages which extend downwardly from the surface to theseam 22; and those passages plus other passages, not shown, define a rowof passages which is parallel to the row that includes the passages 65,68 and 72. The row which includes the passages 73, 76 and 80 willpreferably be spaced from the row which includes the passages 65, 68 and72 by a distance in the range of 6 to 8 feet.

The various passages shown in the drawing will preferably be formed byusing an in-the-hole drill. That drill can, if desired, be made inaccordance with my US. Pat. No. 3,084,673 which was granted Apr. 9,1963.

An air-supplying pipe 92, which has a diameter smaller than the diameterof the passage 72, will be passed downwardly through that passage untilthe lower end of that pipe is disposed just a short distance from theinner end of that passage. Similarly, an air-supplying pipe 93, whichhas a diameter smaller than the diameter of the passage 80, will bepassed downwardly through that passage until the lower end of that pipeis disposed just a short distance from the inner end of that passage.Thereafter, suitable, readily ignitable, combustible material will beforced downwardly through the airsupplying pipes 92 and 93, and thencables with spark plugs at the ends thereof will be forced down throughthose pipes, and arcs will be developed across those spark plugs whilequantities of oxygen are forced downwardly through those pipes. Thereadily'ignited combustible material will respond to the oxygen and tothe arcs to start burning; and that combustible material will be keptburning by forcing air downwardly through the pipes 92 and 93. Theproducts of combustion, which fonn as the combustible material burns,will be drawn upwardly through the space between the air-supplying pipe92 and the inner surface of the passage 72, and through the spacebetween the air-supplying pipe 93 and the inner surface of the passagefill, by connecting the inlet of a heat-resistant blower to the upperends of those passages. The burning of the combustible material adjacentthe inner end of the passage 72 will develop a combustion chamber whichwill tend to expand in all directions and to merge with the inner end ofpassage 64; and, similarly, the burning of the combustible materialadjacent the inner end of the passage will develop a combustion chamberwhich will tend to expand in all directions and to merge with the innerend of the passage 64. Those combustion chambers will quickly expandsufficiently to merge together to form a combined combustion chamber 82;and then the air-supplying pipe 93 can be withdrawn from the passage 80.Thereafter, the air needed to burn the combustible material adjacent thepassages 72 and 80 will be supplied by the pipe 92; and the products ofcombustion from that combustible material will be withdrawn through thepassages 80 and 64.

The continued supplying of air to the pipe 92, and the continuedwithdrawal .of products of combustion from the passages 80 and 64, willcause the combustible material adjacent the inner ends of the passages64, 72 and 80 to burn away. Very quickly, enough of the combustiblematerial will burn away to permit part of the roof of the combustionchamber 82 to crack and crumble; and, thereupon, rubble will fall andpartially fill that combustion chamber. Although that rubble will fillthe portions of the combustion chamber 82 where the inner ends of thepassages 64, 72 and 80 were initially located, the roof of thatcombustion chamber will be strong enough to overhang the portions of thecombustible material which define the existing inner ends of thepassages 64, 72 and 80. As a result, the pipe 92 within the passage 72will be able to continue its air-supplying function, and the passages 64and 80 will be able tocontinue to perform their functions as conduitsfor products of combustion. The air-supplying pipe 92 will gradually bewithdrawn through the passage 72, as the portions of the seam 22 whichdefine the inner end of that passage burn away; and hence thatair-supplying pipe will not be crushed or deformed by the rubble whichfalls into the combustion chamber 82 as succeeding parts of the roof ofthat combustion chamber crumble and crack. This means that theair-supplying pipe 92, the inner end of the passage 72, and the innerends of the passages 64 and 80 will underlie, and will be protected by,the overhanging portion of the roof of the combustion chamber 82.Further, it means that those portions of the seam 22 which are adjacentthe existing inner ends of the passages 64, 72 and 80 will be able tocontinue to burn away.

The burning of the combustible material will continue; and it willextend the combustion chamber 82 along a line which is parallel to thetwo rows of passages which, respectively, include the passages 65, 68and 72 and the passages 73, 76 and 80. That combustion chamber will bewider than the distance between those two rows; and it will merge withthe inner ends of the passages 68 and 76 while it is receiving air fromthe airsupplying pipe 92 in the passage 72 and while products ofcombustion are being withdrawn from the passages 64 and 80. At thattime, the air-supplying pipe 92 will be withdrawn from the passage 72and will be passed downwardly through the passage 68 to supply the airneeded to continue the burning of the combustible material. Also at thattime, the inlet of the heat-resistant blower will be connected to thepassage 76 to withdraw the products of combustion through that passage.

The burning of the combustible material, adjacent the two rows ofpassages which, respectively, include the passages 65 68 and 72 and thepassages 73, 76 and 80, will be continued until an elongated chamber hasbeen formed which extends transversely of, and which merges with theright-hand passages of, the five rows of passages shown in the drawingplus the further rows of passages, not shown, that are parallel to thosefive rows of passages. As the inner end of each passage, in the row ofpassages which includes the passages 65, 68 and 72, is successivelyburned away, the air-supplying pipe 92 will gradually be withdrawn fromthat passage and inserted within the next-succeeding passage in thatrow. if desired, of course, a second air-supplying pipe could beintroduced into the next-succeeding air-supplying passage before theair-supplying pipe 92 was withdrawn from the preceding airisupplyingpassage. As the inner end of each passage, in

the row of passages which includes the passages 73, 76 and 80 issuccessively burned away, the inlet of the heat-resistant blower will bedisconnected from that passage and connected to the next-succeedingpassage in that row. If desired, of course, the inlet of theheat-resistant blowers could be connected to the nextsucceeding passagewhile that inlet was still connected to the immediately precedingpassage. In this way, the combustion chamber 82 will be elongated untilit defines a combustion-supporting chamber that extends transversely of,and that merges with, the inner ends of all of the passages 29, 34, 44,54, 64 and of similar passages in further rows of passages, not shown,within the seam 22 of combustible material. That elongatedcombustion-supporting chamber will act as a header; and, while thelongitudinal center line of that elongated combustion-supporting chambermay be filled with rubble, the portions of that elongatedcombustion-supporting chamber which are immediately adjacent the innerends of the passages 29, 34, 44, 54 and 64 will be overhung by the roofof that elongated combustion-supporting chamber and thus will beessentially free of rubble. This is important; because it will enablethat elongated combustion-supporting chamber to permit air to besupplied through some of the rows of passages and for products ofcombustion to be withdrawn from further rows of passages.

As the elongated combustion-supporting chamber 82 is formed, anair-supplying pipe 90 will be passed downwardly through the passage 54,a further air-supplying pipe, not shown, will be passed downwardlythrough the passage 34, and additional air-supplying pipes, not shown,will be passed downwardly through the right-handmost passage of eacheven-numbered row of passages. The air which passes downwardly throughthose air-supplying pipes will support the burning of the combustiblematerial adjacent the inner ends of the passages in the even-numberedrows of passages; and the resulting products of combustion will bewithdrawn through the passages 29, 44 and 64 and the right-handmostpassages of the other odd-numbered rows of passages.

The supplying of air through the air-supplying pipe 90 and through theother air-supplying pipes in the right-handmost passages of each of theeven-numbered rows of passages and the removal of the products ofcombustion through the righthandmost passages of each of the oddnumbered rows of passages will preferably be begun as the elongatedcombustion-supporting chamber 82 burns into the inner ends of thosepassages. Where that is done, combustion will promptly develop, and thenwill be maintained, along the left-hand face of the full length of theelongated combustion-supporting chamber 82. If, for any reason, it wasdesirable to initiate the burning of the combustible material at theinner ends of the right-hand passages of the various rows of passagesonly after the combustion which had formed the elongatedcombustionsupporting chamber 82 had been completely terminated, thecombustion along the left-hand wall of that elongatedcombustion-supporting chamber could be initiated by passing readilyignitable, combustible material and a cable equipped with a spark plugdown one or more of the even-numbered passages.

As the left-hand face of the elongated combustion-supporting chamber 82burns, it will burn away the portions of the seam 22 which define theinner ends of the passages 29, 34, 44, 54 and 64 and of the right-handpassages, not shown, of the other rows of passages. Moreover, as theleft-hand face burns, the elongated combustion-supporting chamber 82will widen to include the space 84; and, at such time, the roof of theelongated combustion-supporting chamber 82 will tend to crack andcrumble. Thereupon, rubble 86 will fall downwardly within the elongatedcombustion-supporting chamber 82, and the overburden 24 will slumpdownwardly to form a depression w in the surface of the area 20. Thedepression 33 may not be objectionable if it is not unsightly; and,except in low lying ground where it could present some drainageproblems, it need not preclude the resumption of a farm operation. Therubble 86 will not prevent continued burning of the right-hand face ofthe seam 22, will not prevent continued supplying of air to theelongated combustion-supporting chamber, and will not prevent continuedwithdrawal of products of combustion from that elongatedcombustion-supporting chamber; because the roof of the space 84 will bestrong enough to overhand the combustion area by several feet.

As the burning of the right-hand face of the seam 22 continues, theportions of that seam which define the inner ends of the passages 29,34, 44, 54 and 64 and of the right-hand passages, not shown, of theother rows of passages will burn away. At that time, the elongatedcombustion-supporting chamber 82 will merge with the inner ends of thepassages 25, 30, 40, 50 and 60 and of the right-hand passages, notshown, of the other rows of passages. Thereupon, the air-supplying pipe90 and the other air-supplying pipes will be withdrawn from the passagesin which they were disposed and will be introduced into the nextleft-handmost passages to supply air to the elongatedcombustion-supporting chamber 82. The air supplied through thoseair-supplying pipes will enable the combustible material which definesthe passages 25, 30, 40, 50 and 60 and the corresponding passages in theother rows of passages to burn; and, as that combustible material bums,further portions of the roof of the elongated combustion-supportingchamber 82 will crack and crumble. This means that the slump 88 willprogressively shift to the left; but the overhanging portion of the roofof the elongated combustion-supporting chamber 82 will keep the rubble,within that chamber, far enough away from the burning face of the seam22 to enable air to be supplied to, and to permit products of combustionto be withdrawn from, that burning face. As a result, the combustiblematerial in the seam 22 can be progressively burned away, and theproducts of combustion can be passed upwardly through the odd-numberedpassages to the surface.

The burning of the coal or other combustible material of the seam 22will be incomplete essentially producing a gaseous fuel such as carbonmonoxide or hydrogen rather than an incombustible product of combustionsuch as carbon dioxide or water. The carbon monoxide, hydrogen and otherproducts of incomplete combustion will be drawn upwardly to the surfaceby a heat-resistant blower 96 via a conduit 94 which is connected to thevarious odd-numbered passages. That heat-resistant blower will movethose products of incomplete combustion to a utilization area, wherethose components which are desirable as fuels will be separated from therest of the components of the products of incomplete combustion and willbe used to heat water in a boiler. The rest of the components of theproducts of incomplete combustion will be suitably treated to separateout from them any marketable compounds or compositions.

The boiler could be the boiler of any electric generating plant; andthat electric generating plant would be erected close to the middle ofone of the long sides of the area 20. That electric generating plantwould be .displaced far enough from the portion of the area 20 whichoverlies the seam 22 so the slump 88 could not weaken the support forthat electric generating plant; but that electric generating plant wouldbe close enough to the area 20 to minimize the heat losses through thewall of the conduit 94. By locating the electric generating plantimmediately adjacent the area 20, all of the shipping costs associatedwith combustible materials that are mined are avoided. Further, bylocating the electric generating plant immediately adjacent the area 20,the gases which exhaust from that electric generating plant into thesurround ing atmosphere are not immediately added to the air adjacent alarge city. In addition, because the odor-producing and smoke-producingcomponents developed by this process can be removed from the gaseousfuels before those gaseous fuels are burned under the boiler, theexhaust gases from the electric generating plant will contain fewer airpollutants than the exhaust gases from electric generating plants usingsolid fuels.

As soon as any of the passages in the area 20 has performed its functionand its usefulness is ended, the upper end of that passage will besuitably plugged. This means that after the seam 22 has been burnedaway, the area 20 can largely be in the same condition it was before thecombustible material was burned away, except for the slumping of thesurface.

The rate at which the combustible material burns away can be controlledby controlling the rate at which air is introduced into the elongatedcombustion-supporting chamber at the right-hand face of the seam 22. Todetermine how rapidly the combustible material is being burned, smalldiameter observation holes can be drilled down to the seam 22 throughoutthe area 20 and then suitably capped. To ascertain how far the burninghas progressed, it would only be necessary to remove some of the capsand see whether smoke rose out of those observation holes. The rate atwhich the combustible material burns away also could be determined bydisposing thermocouples adjacent the outlet ends of the air-supplyingpipes, and by connecting those thermocouples to a suitable circuit atthe upper ends of those pipes.

Some fly ash will be formed as the combustible material of the seam 22burns away; and that fly ash may tend to lodge within the passages ofthe odd-numbered rows of passages. If the fly ash within those passagestends to accumulate to an undesired degree, the air-supplying pipes canbe removed from the passages of the even-numbered rows of passages andcan be introduced into the passages of the odd-numbered rows ofpassages. At such time, the upper ends of the passages of theodd-numbered rows of passages will be disconnected from the conduit 94,and that conduit will be connected to the upper ends of the passages ofthe even-numbered rows of passages. In addition, air can be forceddownwardly through the annular spaces between the air-supplying pipesand the passages of the odd-numbered rows of passages. The overallresult is that ample air will be available to the burning combustiblematerial, the products of combustion can be readily drawn to thesurface, and some of the fly ash can be driven out of the annular spacesbetween the air-supplying pipes and the passages of the odd-numberedrows of passages. Similarly, if the portions of the right-hand face ofthe seam 22, which define the inner ends of the air-supplying passages,tend to burn away at a rate which is excessively greater than the rateof burning of those portions of the right-hand face of that seam, whichdefine the inner ends of the exhaust passages, the air-supplying pipescan be removed from the air-supplying passages and introduced into theexhaust passages and the exhaust passages can be disconnected from theconduit 94 and that conduit can be connected to the passages of theeven-numbered rows of passages. In this way the burning face of the seam22 can be kept generally straight.

All of this means that the overall rate of burning of the combustiblematerial can be controlled, that the rate of burning of individuallydifferent portions of that combustible material can be controlled, andthat ready withdrawal of the products of incomplete combustion can beattained. This, despite the fact that the seam 22 is always concealedand overlain by the overburden 24.

The present invention makes it possible to utilize many subsurfacecombustible materials that otherwise would not be utilized. For example,the present invention makes it possible to utilize combustible materialsthat are found in the form of shallow seams that could not be minedeconomically by driving shafts or by strip mining. Further, thatinvention makes it possible to utilize combustible materials that haveunduly high percentages of sulfur and of other elements; because severalforms of those elements can be removed before the products of incompletecombustion are burned beneath the boiler. In addition the presentinvention makes it possible to utilize combustible materials that areoverlain by overburdens which could not be stripped economically becauseof unfavorable seam-to-overburden ratios or because of governmentalrestrictions against land disfigurement.

The present invention is particularly useful in mining subsurface coal;but it also is useful in recovering other solid fuels such as ligniteand peat. In addition, the present invention is useful in recovering oilfrom oil wells, wherein the rate at which the oil is normally releasedfrom the oil-bearing sands or rocks is too low to make the pumping ofthe oil economic. Specifically, one or more passages can be formed whichextend downwardly from the surface to the oil-bearing sands or rocks andthen extend substantial distances through those oilbearing sands orrocks in a generally horizontal direction; and combustion can beinitiated and sustained at the inner end of that passage or at the innerends of those passages to heat the oil and thereby reduce the viscosityof that oil to the point where that oil will be able to drain out of theoil-bearing sands or rocks. In some instances, the combustion can besustained by air and by the oil which drains out of the oil-bearingsands or rocks; but, in other instances, the combustion will have to besustained byair and by gaseous fuel which is forced downwardly to theinner end of a passage through a suitable pipe. In all instances, someof the oil will be vaporized and some of the oil will be incompletelyburned to form combustible products of combustion; and the vaporized oiland the combustible products of combustion will be drawn to the surfacefor suitable treatment and use. The vaporized oil and the combustibleproducts of combustion will heat the walls of the horizontally extendingportions of the passage or passages; and hence substantial amounts ofoil can be recovered. As the oil adjacent the inner end of the passageor adjacent the inner ends of the passages is recovered, the area ofcombustion will be moved toward the outer end of that passage or towardthe outer ends of those passages. Consequently, it should be apparentthat the present invention provides an important and useful method ofmining or recovering various kinds of subsurface materials.

Referring particularly to FIGS. 6 and 7, the numeral denotes ahorizontally directed shaft in a subsurface seam of combustiblematerial. The numerals 102 and 106 denote passages which are disposedahead of that shaft and which extend downwardly from the surface andpenetrate that seam. The passages 102 and 106 are representative of anumber of passages which are generally aligned to constitute a row ofpassages ahead of the shaft 100. The numerals 108 and 112 denote furtherpassages which are disposed ahead of the shaft 100 and which extenddownwardly from the surface and penetrate the seam in which that shafthas been driven. The passages 108 and 112 are representative of a numberof passages which are generally aligned to constitute a second row ofpassages ahead of the shaft 100. The passages 102 and 108 are disposedwholly forwardly of the shaft 100; and, initially, the passages 106 and112 were disposed wholly forwardly of that shaft. However, as theworking face of the shaft 100 was advanced, it merged with the innerends of the passages 106 and 112.

The inner endof the passage 102 laps part of the horizontally directedportion of the passage 106. Similarly, the inner end of the passage 108laps part of the horizontally directed portion of the passage 112. Theinner ends of the passages 102, 106, 108 and 112-will pass through, orclose to, any large pockets which are disposed forwardly of the shaft100 and which contain noxious gases.

The numeral 118 denotes a gas-moving device; and a conduit 116 extendsbetween the inlet of that gas-moving device and the upper ends of thepassages 102 and 108. Initially that conduit connected the inlet of thatgas-moving device to the upper ends of the passages 106 and 112; and itserved to draw out of those passages any noxious gases that enteredthose passages from pockets which were intersected by, or were close to,those passages. However, after the working face of the shaft 100 mergedwith the passages 106 and 112, the conduit 116 was disconnected from theupper ends of those passages and was then connected to the upper ends ofthe passages 102 and 103. Also, plugs 114 were used to close the upperends of the passages 106 and 112 after the working face of the shaft 100merged with the inner ends of those passages.

The gas-moving device 11% will maintain reduced pressures within thepassages 102 and 108, and thus will tend to withdraw from thosepassages, and from the seam ahead of the shaft 100, any noxious gases inlarge pockets ahead of the working face of that shaft. Those reducedpressures will, of course, withdraw any noxious gases from pockets whichare directly intersected by the passages 102 and 108; but those reducedpressures also can withdraw noxious gases from large pockets which areclose to those passages. Specifically, those reduced pressures willwithdraw noxious gases from any large pockets which are spaced from thepassages 102 and 108 but which are in communication with those passagesvia cracks or fissures in the seam or via porous material in that seam.Also, if the blasting at the working face of the shaft 100 tends to formcracks or fissures which communicate with the passages 1 i102 and thosepassages will be able to withdraw any noxious gases which entered thosecracks and fissures. By maintaining reduced pressures ahead of theworking face of the shaft 100, the present invention minimizes, and caneven prevent, the likelihood of any noxious gases entering that shaft.

Whereas the drawing and accompanying description have shown anddescribed two preferred embodiments of the present invention it shouldbe apparent to those skilled in the art that various changes may be madein the form of the invention without affecting the scope thereof.

Iclaim: I

1. The method of burning subsurface combustible material in situ thatcomprises:

drilling a passage which extends downwardly from the surface to saidcombustible material and then extends a substantial distance throughsaid combustible material in a generally horizontal direction;

drilling a second passage which extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said second passage being spaced from the first said passage but thegenerally horizontal portion of said second passage being generally atthe same level as, and being generally parallel to, the generallyhorizontal portion of said first said passage;

igniting the combustible material adjacent the inner ends of saidpassages to cause a portion of said combustible material to burn awayand thereby form a combustion chamber within said combustible materialwhich extends transversely of said first said and said second passagesand which interconnects said inner ends of said first said and saidsecond passages;

removing products of combustion. of said combustible material from saidcombustion chamber through said second passage;

said generally horizontal portions of said first said and said secondpassages being overlain by an overburden;

the portion of said overburden adjacent to the inner ends of said firstsaid and said second passages providing a selfsupporting overhang whichenables air to enter said combustion chamber from said first saidpassage and which enables products of combustion to move to andoutwardly through said second passage;

said air supplied to said combustion chamber by said first said passagecausing that wall of said combustion chamber which is adjacent to saidinner ends of said first said and said second passages to burn away andcause said combustion chamber to progressively move" along the lengthsof said generally horizontal portions of said first said and said secondpassages while continuing to interconnect said inner ends of said firstsaid and said second passages; and

portions of said overburden adjacent to the opposite wall of saidcombustion chamber slumping down into said combustionchamber, but saidportion of said overburden adjacentto said inner ends of said first saidand said second passages enabling air to continue to enter saidcombustion chamber from said first said passage and enabling products ofcombustion to move to and outwardly through said second passage.

2. The method of burning subsurface combustible material in situ asclaimed in claim 1 wherein a reduced pressure is maintained at the upperend of said second passage to facilitate the removal of said products ofcombustion of said combustible material, from said combustion chamber,through said second passage.

3. The method of burning subsurface combustible material in situ thatcomprises:

drilling a passage which extends downwardly from the surface to saidcombustible material-and then extends a substantial distance throughsaid combustible material in a generally horizontal direction;

drilling a second passage which extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said second passage being spaced from the first said passage but thegenerally horizontal portion of said second passage being generally atthe same level as, and being generally parallel to, the generallyhorizontal portion of said first said passage;

igniting the combustible material adjacent the inner ends of saidpassages to cause a portion of said combustible material to burn awayand thereby form a combustion chamber within said combustible materialwhich extends transversely of said first said and said second passagesand. which interconnects said inner ends of said first said and saidsecond passages;

supplying air, -to the combustible material defining the walls of saidcombustion chamber, through said first said passage;

removing products of combustion of said combustible material from saidcombustion chamber through said second passage;

said generally horizontal portions of said first said and said secondpassages being overlain by an overburden;

the portion of said overburden adjacent to the inner ends of said firstsaid and said second passages providing a selfsupporting overhang whichenables air to enter said combustion chamber from said first saidpassage and which enables products of combustion to move to andoutwardly through said second passage;

said air supplied to said combustion chamber by said first said passagecausing that wall of said combustion chamber which is adjacent to saidinner ends of said first said and said second passages to burn away andcause said combustion chamber to progressively move" along the lengthsof said generally horizontal portions of said first said and said secondpassages while continuing to interconnect said inner ends of said firstsaid and said second passages;

portions of said overburden adjacent to the opposite wall of saidcombustion chamber slumping down into said combustion chamber, but saidportion of said overburden adjacent to said inner ends of said firstsaid and said second passages enabling air to continue to enter saidcombustion chamber from said first said passage and enabling products ofcombustionv to move to and outwardly through said second passage;

subsequently supplying air to said combustible material,

which defines said walls of said combustion chamber, through said secondpassage;

removing products of combustion, of said combustible material, from saidcombustion chamber, through said first said passage; and

the resulting flow of air and products of combustion through saidcombustion chamber, from said inner end of said second passage to saidinner end of said first said passage, increasing the rate of burning ofthe portion of the first said wall of said combustion chamber which isadjacent to said inner end of said second passage.

4. The method of bumin'g'subsrirface combustible material in situ thatcomprises:

drilling a passage which extends downwardly from the surface to saidcombustible material and then extends a substantial distance throughsaid combustible material in a generally horizontal direction;

drilling a second passage which extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said second passage being spaced from the first said passage;

igniting the combustible material adjacent the inner ends of saidpassages;

supplying air to said combustible material through the first saidpassage;

removing products of combustion of said combustible material throughsaid second passage;

drilling a third passage so it extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said third passage having the inner end thereof lapping part of saidfirst said passage so the burned out area in said combustible materialwill merge with said third passage before it moves wholly away from saidfirst said passage;

drilling a fourth passage so it extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;and

said fourth passage having the inner end thereof lapping part of saidsecond passage so said burned out area will merge with said fourthpassage before it moves wholly away from said second passage.

5. The method of burning subsurface combustible material in situ thatcomprises:

drilling a passage which extends downwardly from the surface to saidcombustible material and then extends a substantial distance throughsaid combustible material in a generally horizontal direction;

drilling a second passage which extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said second passage being spaced from the first said passage;

igniting the combustible material adjacent the inner ends of saidpassages;

supplying air to said combustible material through the first saidpassage;

removing products of combustion of said combustible material throughsaid second passage;

drilling a third passage so it extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said third passage having the inner end thereof lapping part of saidfirst said passage so the burned out area in said combustible materialwill merge with said third passage before it moves wholly away from saidfirst said passage;

drilling a fourth passage so it extends downwardly from said surface tosaid combustible material and then extends a substantial distancethrough said combustible material in a generally horizontal direction;

said fourth passage having the inner end thereof lapping part of saidsecond passage so said burned out area will merge with said fourthpassage before it moves wholly away from said second passage;

said third passage being drilled so it coacts with said first saidpassage to define a row of passages; and

said fourth passage being drilled so it coacts with said second passageto define a second row of passages which is spaced from, but generallyparallel to, the first said row of passages.

6. The method of bunting subsurface combustible material in situ' whichcomprises:

drilling a row of passages which extend downwardly from the surface tosaid combustible material and then extend substantial distances throughsaid combustible material in a generally horizontal direction;

drilling the passages of said row of passages so they overlap in part;drilling a second row of passages which extend downwardly from saidsurface to said combustible material and then extend substantialdistances through said combustible material in a generally horizontaldirection;

drilling the passages of said second row of passages so they overlap inpart;

said second row of passages being formed so it is spaced from butgenerally parallel to the first said row of passages;

drilling a further row of passages which extend downwardly from saidsurface to said combustible material and then extend substantialdistances through said combustible material in a generally horizontaldirection;

said further row of passages being drilled so it is close to, but

is directed transversely of, said first said and said second row ofpassages; using said further row of passages to burn out the combustiblematerial adjacent the inner ends of the passages of said first andsecond row of passages and thereby form an elongatedcombustion-supporting chamber in said combustible material which isclose to, but is directed transversely of, said first said and saidsecond row of passages;

supplying air to at least one passage of said first said row of passagesand applying a reduced pressure to the upper end of at least one passageof said second row of passages to promote burning of the combustiblematerial forming one face of said elongated combustion-supportingchamber; and

subsequently supplying air to a further passage of said first said rowof passages and applying a reduced pressure to the upper end of afurther passage of said second row of passages to continue to promoteburning of the combustible material forming one face of said elongatedcombustion-supporting chamber.

7. The combination of a small diameter drilled passage that curvesdownwardly from the surface of an area to a subsurface seam, saidpassage having an elongated portion that extends a substantial distancethrough said seam in a direction generally parallel to said seam, agas-moving device at said surface of said area, and a conduit thatextends between the upper end of said passage and the inlet of saidgas-moving device, said gasmoving device maintaining a reduced pressurewithin said passage, said passage performing the dual functions ofcollecting gases withdrawn from said subsurface seam by said reducedpressure within said passage and of then conducting said gases to saidsurface of saidarea.

8. The combination claimed in claim 7 wherein the inner end of saidpassage extends toward a working driven into said seam, and wherein saidreduced pressure within said passage will withdraw noxious gases fromany large pockets that are within said seam and that are located aheadof said working and that are intersected by said passage.

9. The combination of a small diameter drilled passage that curvesdownwardly from the surface of an area to a subsurface seam, saidpassage having an elongated portion that extends a substantial distancethrough said seam in a direction generally parallel to said seam, a gasmoving device at said surface of said area, a second small diameterdrilled passage that curves downwardly from said surface of said area tosaid subsurface seam, said second passage having an elongated portionthat extends a substantial distance through said seam in a directiongenerally parallel to said seam, said elongated portion of said secondpassage being spaced from but being generally parallel to and beinggenerally coextensive with said elongated portion of the first saidpassage, a combustion-supporting chamber within said seam which extendstransversely of said first said and said second passages and whichinterconnects the inner ends of said first said and said secondpassages, a source of pressurized air connected to the upper end of saidsecond passage, and a conduit that extends between the upper end of saidfirst said passage and the inlet of said gas-moving device, said sourceof pressurized air and said second passage supplying air to saidcombustion chamber, said gas-moving device maintaining a reducedpressure within said first said passage and products of combustionwithin said combustion-supporting chamber responding to said reducedpressure within said first said passage to pass upwardly from saidcombustion-supporting chamber to said gas-moving device 110. The methodof maintaining a reduced pressure throughout a substantial area within asubsurface seam which comprises drilling a small diameter passage thatcurves downwardly from the surface to said seam, extending the inner endof said passage a substantial distance through said seam in a directiongenerally parallel to said seam, connecting the upper end of saidpassage to the inlet of a gas-moving device, and operating saidgas-moving device to withdraw gas from said upper end of said passageand thereby maintain a reduced pressure within said passage, saidpassage performing the dual functions of collecting gases withdrawn fromsaid subsurface seam by said reduced pressure within said passage and ofthen conducting said gases to said surface of said area.

11. The method of maintaining a reduced pressure throughout asubstantial area within a subsurface seam as claimed in claim whereinsaid passage is drilled so the inner end thereof extends toward aworking driven into said seam, and wherein gases from pockets that arein said seam ahead of said working and that are intersected by saidpassage pass upwardly through said passage to said gas-moving device.

12. The method of maintaining a reduced pressure throughout asubstantial area within a subsurface seam which comprises drilling asmall diameter passage that curves downwardly from the surface to saidseam, extending the inner end of said passage a substantial distancethrough said seam in a direction generally parallel to said seam,connecting the upper end of said passage to the inlet of a gas-movingdevice, drilling a second small diameter passage that curves downwardlyfrom said surface to said seam, extending the inner end of said passagea substantial distance through said seam in a direction generallyparallel to said seam, drilling said second passage so said inner endthereof is spaced from but is generally parallel to and is generallycoextensive with said inner end of said first said passage, acombustion-supporting chamber within said seam, supplying air to theupper end of said second passage to cause said air to pass to saidcombustion-supporting chamber, and operating said gas-moving device tocause products of combustion from said combustion-supporting chamber topass upwardly through said first said passage to said gas-moving device.

13. The method of recovering subsurface material in situ that comprises:

drilling a passage which extends downwardly from the surface to saidmaterial and then extends a substantial distance through said materialin a generally horizontal direction;

initiating and sustaining combustion adjacent the inner end of saidpassage to vaporize part of said material and to incompletely bum partof said material;

the vaporizing of part of said material and incomplete burning of partof said material forming a combustion chamber within said material incommunication with said inner end of said passage;

the horizontally extending portion of said passage being overlain by anoverburden;

the portion of said overburden adjacent said inner end of said passageproviding a self-supporting overhang which enables air to enter saidcombustion chamber and which enables said vaporized portion of saidmaterial and the products of incomplete combustion of said material toflow through and out of said combustion chamber; supplying pressurizedair to said combustion chamber to cause that wall of said combustionchamber which is adjacent said inner end of said passage to volatilizeand to incompletely burn and thereby cause said combustion chamber tomov e" along the length of said horizontally extending portion of saidpassage; and

withdrawing said vaporized portion of said material and the products ofincomplete combustion of said material to the surface for utilizationthereof; and

portions or said overburden adjacent the opposite wall of saidcombustion chamber slumping down into said combustion chamber, but saidportion of said overburden adjacent said inner end of said passageenabling air to continue to enter said combustion chamber and enablingsaid vaporized portion of said material and the products of incompletecombustion of said material to flow through and out of said combustionchamber.

14. The method of recovering subsurface material in situ as claimed inclaim 13 wherein said material is oil that normally has too high aviscosity to freely drain out of the oil-bearing sands or rocks in whichit is held, and wherein said combustion warms said oil and reduces theviscosity thereof sufficiently to enable said oil to drain from saidoil-bearing sands or rocks.

15. The method of recovering subsurface material in situ as claimed inclaim 13 wherein said material is oil that normally has too high aviscosity to freely drain out of the oil-bearing sands or rocks in whichit is held, and wherein said vaporized portion of said material and theproducts of incomplete combustion of said material warm the walls ofsaid passage and thereby enable the oil held within said walls of saidpassage to drain away from said walls.

2. The method of burning subsurface combustible material in situ asclaimed in claim 1 wherein a reduced pressure is mAintained at the upperend of said second passage to facilitate the removal of said products ofcombustion of said combustible material, from said combustion chamber,through said second passage.
 3. The method of burning subsurfacecombustible material in situ that comprises: drilling a passage whichextends downwardly from the surface to said combustible material andthen extends a substantial distance through said combustible material ina generally horizontal direction; drilling a second passage whichextends downwardly from said surface to said combustible material andthen extends a substantial distance through said combustible material ina generally horizontal direction; said second passage being spaced fromthe first said passage but the generally horizontal portion of saidsecond passage being generally at the same level as, and being generallyparallel to, the generally horizontal portion of said first saidpassage; igniting the combustible material adjacent the inner ends ofsaid passages to cause a portion of said combustible material to burnaway and thereby form a combustion chamber within said combustiblematerial which extends transversely of said first said and said secondpassages and which interconnects said inner ends of said first said andsaid second passages; supplying air, to the combustible materialdefining the walls of said combustion chamber, through said first saidpassage; removing products of combustion of said combustible materialfrom said combustion chamber through said second passage; said generallyhorizontal portions of said first said and said second passages beingoverlain by an overburden; the portion of said overburden adjacent tothe inner ends of said first said and said second passages providing aself-supporting overhang which enables air to enter said combustionchamber from said first said passage and which enables products ofcombustion to move to and outwardly through said second passage; saidair supplied to said combustion chamber by said first said passagecausing that wall of said combustion chamber which is adjacent to saidinner ends of said first said and said second passages to burn away andcause said combustion chamber to progressively ''''move'''' along thelengths of said generally horizontal portions of said first said andsaid second passages while continuing to interconnect said inner ends ofsaid first said and said second passages; portions of said overburdenadjacent to the opposite wall of said combustion chamber slumping downinto said combustion chamber, but said portion of said overburdenadjacent to said inner ends of said first said and said second passagesenabling air to continue to enter said combustion chamber from saidfirst said passage and enabling products of combustion to move to andoutwardly through said second passage; subsequently supplying air tosaid combustible material, which defines said walls of said combustionchamber, through said second passage; removing products of combustion ofsaid combustible material, from said combustion chamber, through saidfirst said passage; and the resulting flow of air and products ofcombustion through said combustion chamber, from said inner end of saidsecond passage to said inner end of said first said passage, increasingthe rate of burning of the portion of the first said wall of saidcombustion chamber which is adjacent to said inner end of said secondpassage.
 4. The method of burning subsurface combustible material insitu that comprises: drilling a passage which extends downwardly fromthe surface to said combustible material and then extends a substantialdistance through said combustible material in a generally horizontaldirection; drilling a second passage which extends downwardly from saidsurface to said combustible material and then extends a substantialdistance through said combustible material in a generally horizontaldirection; said second passaGe being spaced from the first said passage;igniting the combustible material adjacent the inner ends of saidpassages; supplying air to said combustible material through the firstsaid passage; removing products of combustion of said combustiblematerial through said second passage; drilling a third passage so itextends downwardly from said surface to said combustible material andthen extends a substantial distance through said combustible material ina generally horizontal direction; said third passage having the innerend thereof lapping part of said first said passage so the burned outarea in said combustible material will merge with said third passagebefore it moves wholly away from said first said passage; drilling afourth passage so it extends downwardly from said surface to saidcombustible material and then extends a substantial distance throughsaid combustible material in a generally horizontal direction; and saidfourth passage having the inner end thereof lapping part of said secondpassage so said burned out area will merge with said fourth passagebefore it moves wholly away from said second passage.
 5. The method ofburning subsurface combustible material in situ that comprises: drillinga passage which extends downwardly from the surface to said combustiblematerial and then extends a substantial distance through saidcombustible material in a generally horizontal direction; drilling asecond passage which extends downwardly from said surface to saidcombustible material and then extends a substantial distance throughsaid combustible material in a generally horizontal direction; saidsecond passage being spaced from the first said passage; igniting thecombustible material adjacent the inner ends of said passages; supplyingair to said combustible material through the first said passage;removing products of combustion of said combustible material throughsaid second passage; drilling a third passage so it extends downwardlyfrom said surface to said combustible material and then extends asubstantial distance through said combustible material in a generallyhorizontal direction; said third passage having the inner end thereoflapping part of said first said passage so the burned out area in saidcombustible material will merge with said third passage before it moveswholly away from said first said passage; drilling a fourth passage soit extends downwardly from said surface to said combustible material andthen extends a substantial distance through said combustible material ina generally horizontal direction; said fourth passage having the innerend thereof lapping part of said second passage so said burned out areawill merge with said fourth passage before it moves wholly away fromsaid second passage; said third passage being drilled so it coacts withsaid first said passage to define a row of passages; and said fourthpassage being drilled so it coacts with said second passage to define asecond row of passages which is spaced from, but generally parallel to,the first said row of passages.
 6. The method of burning subsurfacecombustible material in situ which comprises: drilling a row of passageswhich extend downwardly from the surface to said combustible materialand then extend substantial distances through said combustible materialin a generally horizontal direction; drilling the passages of said rowof passages so they overlap in part; drilling a second row of passageswhich extend downwardly from said surface to said combustible materialand then extend substantial distances through said combustible materialin a generally horizontal direction; drilling the passages of saidsecond row of passages so they overlap in part; said second row ofpassages being formed so it is spaced from but generally parallel to thefirst said row of passages; drilling a further row of passages whichextend downwardly from said surfaCe to said combustible material andthen extend substantial distances through said combustible material in agenerally horizontal direction; said further row of passages beingdrilled so it is close to, but is directed transversely of, said firstsaid and said second row of passages; using said further row of passagesto burn out the combustible material adjacent the inner ends of thepassages of said first and second row of passages and thereby form anelongated combustion-supporting chamber in said combustible materialwhich is close to, but is directed transversely of, said first said andsaid second row of passages; supplying air to at least one passage ofsaid first said row of passages and applying a reduced pressure to theupper end of at least one passage of said second row of passages topromote burning of the combustible material forming one face of saidelongated combustion-supporting chamber; and subsequently supplying airto a further passage of said first said row of passages and applying areduced pressure to the upper end of a further passage of said secondrow of passages to continue to promote burning of the combustiblematerial forming one face of said elongated combustion-supportingchamber.
 7. The combination of a small diameter drilled passage thatcurves downwardly from the surface of an area to a subsurface seam, saidpassage having an elongated portion that extends a substantial distancethrough said seam in a direction generally parallel to said seam, agas-moving device at said surface of said area, and a conduit thatextends between the upper end of said passage and the inlet of saidgas-moving device, said gas-moving device maintaining a reduced pressurewithin said passage, said passage performing the dual functions ofcollecting gases withdrawn from said subsurface seam by said reducedpressure within said passage and of then conducting said gases to saidsurface of said area.
 8. The combination claimed in claim 7 wherein theinner end of said passage extends toward a working driven into saidseam, and wherein said reduced pressure within said passage willwithdraw noxious gases from any large pockets that are within said seamand that are located ahead of said working and that are intersected bysaid passage.
 9. The combination of a small diameter drilled passagethat curves downwardly from the surface of an area to a subsurface seam,said passage having an elongated portion that extends a substantialdistance through said seam in a direction generally parallel to saidseam, a gas-moving device at said surface of said area, a second smalldiameter drilled passage that curves downwardly from said surface ofsaid area to said subsurface seam, said second passage having anelongated portion that extends a substantial distance through said seamin a direction generally parallel to said seam, said elongated portionof said second passage being spaced from but being generally parallel toand being generally coextensive with said elongated portion of the firstsaid passage, a combustion-supporting chamber within said seam whichextends transversely of said first said and said second passages andwhich interconnects the inner ends of said first said and said secondpassages, a source of pressurized air connected to the upper end of saidsecond passage, and a conduit that extends between the upper end of saidfirst said passage and the inlet of said gas-moving device, said sourceof pressurized air and said second passage supplying air to saidcombustion chamber, said gas-moving device maintaining a reducedpressure within said first said passage and products of combustionwithin said combustion-supporting chamber responding to said reducedpressure within said first said passage to pass upwardly from saidcombustion-supporting chamber to said gas-moving device
 10. The methodof maintaining a reduced pressure throughout a substantial area within asubsurface seam which comprises drilling a small diameter passage thatcurVes downwardly from the surface to said seam, extending the inner endof said passage a substantial distance through said seam in a directiongenerally parallel to said seam, connecting the upper end of saidpassage to the inlet of a gas-moving device, and operating saidgas-moving device to withdraw gas from said upper end of said passageand thereby maintain a reduced pressure within said passage, saidpassage performing the dual functions of collecting gases withdrawn fromsaid subsurface seam by said reduced pressure within said passage and ofthen conducting said gases to said surface of said area.
 11. The methodof maintaining a reduced pressure throughout a substantial area within asubsurface seam as claimed in claim 10 wherein said passage is drilledso the inner end thereof extends toward a working driven into said seam,and wherein gases from pockets that are in said seam ahead of saidworking and that are intersected by said passage pass upwardly throughsaid passage to said gas-moving device.
 12. The method of maintaining areduced pressure throughout a substantial area within a subsurface seamwhich comprises drilling a small diameter passage that curves downwardlyfrom the surface to said seam, extending the inner end of said passage asubstantial distance through said seam in a direction generally parallelto said seam, connecting the upper end of said passage to the inlet of agas-moving device, drilling a second small diameter passage that curvesdownwardly from said surface to said seam, extending the inner end ofsaid passage a substantial distance through said seam in a directiongenerally parallel to said seam, drilling said second passage so saidinner end thereof is spaced from but is generally parallel to and isgenerally coextensive with said inner end of said first said passage, acombustion-supporting chamber within said seam, supplying air to theupper end of said second passage to cause said air to pass to saidcombustion-supporting chamber, and operating said gas-moving device tocause products of combustion from said combustion-supporting chamber topass upwardly through said first said passage to said gas-moving device.13. The method of recovering subsurface material in situ that comprises:drilling a passage which extends downwardly from the surface to saidmaterial and then extends a substantial distance through said materialin a generally horizontal direction; initiating and sustainingcombustion adjacent the inner end of said passage to vaporize part ofsaid material and to incompletely burn part of said material; thevaporizing of part of said material and incomplete burning of part ofsaid material forming a combustion chamber within said material incommunication with said inner end of said passage; the horizontallyextending portion of said passage being overlain by an overburden; theportion of said overburden adjacent said inner end of said passageproviding a self-supporting overhang which enables air to enter saidcombustion chamber and which enables said vaporized portion of saidmaterial and the products of incomplete combustion of said material toflow through and out of said combustion chamber; supplying pressurizedair to said combustion chamber to cause that wall of said combustionchamber which is adjacent said inner end of said passage to volatilizeand to incompletely burn and thereby cause said combustion chamber to''''move'''' along the length of said horizontally extending portion ofsaid passage; and withdrawing said vaporized portion of said materialand the products of incomplete combustion of said material to thesurface for utilization thereof; and portions or said overburdenadjacent the opposite wall of said combustion chamber slumping down intosaid combustion chamber, but said portion of said overburden adjacentsaid inner end of said passage enabling air to continue to enter saidcombustion chamber and enabling said vaporized portion of said materialand the prodUcts of incomplete combustion of said material to flowthrough and out of said combustion chamber.
 14. The method of recoveringsubsurface material in situ as claimed in claim 13 wherein said materialis oil that normally has too high a viscosity to freely drain out of theoil-bearing sands or rocks in which it is held, and wherein saidcombustion warms said oil and reduces the viscosity thereof sufficientlyto enable said oil to drain from said oil-bearing sands or rocks. 15.The method of recovering subsurface material in situ as claimed in claim13 wherein said material is oil that normally has too high a viscosityto freely drain out of the oil-bearing sands or rocks in which it isheld, and wherein said vaporized portion of said material and theproducts of incomplete combustion of said material warm the walls ofsaid passage and thereby enable the oil held within said walls of saidpassage to drain away from said walls.